In the field of medical analyses, pathological states, defined as inflammatory, are ascertained by measuring also the speed of sedimentation of the corpuscular part of the blood (ESR).
Known methods to measure ESR are generally characterized by long analysis times (from 30 to 60 minutes), which prevent such analysis being performed in succession with other, faster analyses, for example cell-counter analyses.
Moreover, known methods generally have to use throw-away containers, which entails an increase in costs both for purchasing them and for their disposal. Furthermore, a great quantity of blood is needed to perform the analysis, normally from 1 to 3 ml, and this entails problems in particular cases, for example when the analysis is to be made on children.
A method to detect the ESR is known, proposed by the same Applicant in EP-A-1.098.188, which provides to take a sample of blood to be analyzed, not diluted and to which no anti-coagulants or other substances have been added, from a container in which it is preserved, and to introduce this sample into a capillary tube, which is used for various measurements made on different samples.
This method is based on detecting the optical density or absorbance of the blood at a point of the measurement volume, by instantaneously stopping the flow of blood inside the capillary, in which a photometric signal correlated to the ESR examination is detected, according to the reference method known as Westergren (see for example the article “Determination of the Length of Sedimentation Reaction . .” by Piva E., Fassina P. and Plebani M., published in Clin. Chem. Lab. Med. 2002; 40(7); pages 713-717)
The study of absorbance over time allows to work out the ERS value by eliminating the initial dead times, and thus considerably reducing the overall times needed, and obviating the need to use throw-away containers for the analysis. Moreover, the necessary quantity of blood to be analyzed is smaller and hence the analysis can be carried out without difficulty even on pediatric patients.
Another known method for determining the speed of sedimentation of blood is described in EP-A-0.732.576, also in the name of the present Applicant. Here too, the method uses the detection of the optical density, or absorbance, of a blood sample at a point of the measurement volume while said sample is subjected to centrifugal rotation inside a capillary tube.
The study of the absorbance in the blood sample subjected to analysis allows to find other parameters too, correlated to the speed of sedimentation, such as viscosity, elasticity or density, as indicated particularly in EP'188.
Moreover, the characteristics and peculiarities of the analysis made in this way, particularly the use of a blood sample in movement inside a tube, the non-use of throw-away containers and the extremely rapid response times, have led the present Applicant to hypothesize that it can be integrated, in line and with sequential measurements, with other types of hematological analyses, such as for example the analysis made by cell-counters.
Cell-counters are a category of measuring instruments used in clinical analysis laboratories which provide the fundamental parameters of hematology, such as counting red corpuscles, white corpuscles, platelets, hematocrit, and other parameters concerning the form and size of the corpuscle part of the blood. In order to perform this analysis, the machine uses a so-called primary blood sample, taken from the patient and collected in a sealed container which has a top that can be perforated by a needle in order to pick up the sample to be analyzed.
It must be considered that, in diagnostic techniques, the analysis performed by the cell-counters has always been considered not compatible time-wise with what is connected to measuring ESR, and hence also with reference to the parameters of viscosity, elasticity, density or similar, which can be obtained from the study of absorbance as proposed in EP'188 and EP'576.
In fact, in the state of the art, and before the method to measure ESR as described in EP'188 was developed, the producers of cell-count machines had never thought of integrating such machines and the devices used to measure the speed of blood sedimentation into a single apparatus, because of the intrinsic obstacles and incompatibilities as pointed out above.
It should also be noted that the usual and traditional techniques for measuring ESR use diluted blood, mixed with anti-coagulants which are not compatible with subsequent analyses such as those concerning the cell-count, whereas the technique described in EP'188 uses a dry state anti-coagulant (EDTA) which is the same as that used in primary test tubes used for cell-count analyses.
Document WO-A-95/14224 describes an apparatus that uses the measurement obtained by a cell-counter in order to find, empirically and by means of calculations, the ESR value. To be more exact, the apparatus provides a first analysis section wherein a blood sample is sent to a measuring cell provided with four electrodes, inside which the electric impedance of the blood sample is measured.
In a second analysis section another blood sample is subjected, possibly after being suitably mixed with a diluting product, to a step to determine the hematocrit. It is necessary to use another blood sample in an apparatus of this type since the measurement of the impedance, performed in the first analysis section, alters the sample irreversibly, which cannot therefore be used in sequence and in line to perform the measurement of the hematocrit too.
The data relating to the impedance of the blood and its hematocrit, plus the value of the temperature relating to the impedance measuring cell as measured by a suitable measuring element, are sent to a processing unit that calculates empirically, from these data, the ESR value.
The limits and disadvantages of an apparatus of this type are first of all its complexity and the large number of components it requires, both to detect the parameters and also to calculate and process the data.
Above all, however, the result obtained does not guarantee reliability and precision, on the one hand because intrinsically the empirical calculation process does not allow to ensure that precise values are obtained, and on the other hand because it adds together errors of tolerance due to no fewer than three different measuring systems.
It must in any case be considered that, in substance, this known apparatus does not perform an analytical and reliable measurement, in line, in sequence, and with the same blood sample, both of the speed of blood sedimentation and also of the hematocrit.
The purpose of the invention is therefore to achieve a device and propose a relative method to perform hematological analyses which integrates, in a single apparatus—small, compact and easy to transport—the functions of measuring, in line, in close sequence and with the same blood sample, the speed of blood sedimentation (ESR) in a machine able to perform at least the cell-count function and/or other connected analyses.
The Applicant has devised and embodied the present invention in order to obtain this purpose and other advantages as shown hereafter.